METABOLIC PROPERTIES OF A PURIFIED PREPARATION OF LARGE FRAGMENTS OF THE CEREBELLAR GLOMERULI: GLUCOSE METABOLISM AND AMINO ACID UPTAKE

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Abstract
—: Glomerulus particle preparations contain large fragments of the cerebellar glomeruli and are composed almost exclusively of well‐defined neuronal processes (Balázs et al., 1975). The metabolic competence of the glomerulus particles was demonstrated by their ability to convert [14C]glucose to 14CO2 and lactate at a linear rate for over 1 h. The preparations also transported deoxyglucose via an high affinity uptake system (KT= 0.2‐0.5 mM).The kinetics of uptake of various labelled amino acids were also studied. Apparently high affinity uptake systems (KT values about 10‐5 M) were found for thc putative transmitters GABA, glycine, glutamate, and aspartate, but not for leucine, serine, and tyrosine. The maximal velocity of high affinity uptake was the greatest for GABA (about 15 nmol/mg protein per 10 min), while glycine was taken up at about 50%, and aspartate and glutamate at only 13% of the rate obtained with GABA. High affinity uptake of glycine required Na+ (half maximal uptake at 70 mM‐NaCl). Inhibition of glucose transport and glycolysis, electron transport, or oxidative phosphorylation also depressed high affinity uptake of glycine. 2,4‐Diaminobutyric acid was a potent competitive inhibitor of GABA uptake (K1 approx 22 μM), while β‐alanine and glycine had a relatively minor inhibitory effect on the uptake of GABA.